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Production and Quality

Production and Quality

What are the contact forms when using the pressing ring and spacer to fix the lens?

What are the contact forms among the concave-convex lens, the pressing ring and the spacer when using the pressing ring and spacer to fix the lens? According to the summary of scholars and research institutions at home and abroad, there are five main contact forms among the pressing ring, the spacer and the concave-convex lens: sharp corner, tangential, toroidal, spherical, and oblique plane. 1) Sharp corner interface On a pressing ring or spacer, a curved surface with a radius of about 0.05mm is ground at the intersection of the end face and the cylindrical surface. The ground surface is called the sharp corner interface, and its contact form is as follows:2) Tangential interface The interface formed by the contact between the surface of the convex lens and the surface of the pressing ring or the spacer is a tangential interface. Different from the sharp corners, the tangential interface is not used to fix the concave spherical lens, but the convex spherical lens.3) Toroidal interface The following figure shows the contact form of the toroidal interface.4) Spherical interface The spherical interface contact form is that the metal pressing ring or spacer is in seamless contact with the spherical surface of the lens. Because the axial load is evenly distributed on the spherical contact surface, there is no pressure concentration in principle. However, the assembly precision of this contact form is particularly high, and the lens and the metal pressing ring must be machined with high precision, so it is difficult for average companies to accept it due to the high cost.5) Oblique plane interface As shown in the figure below, the oblique plane interface is the same as the spherical interface with a comparatively big contact area, so that the contact pressure generated by thrust load is distributed evenly. But its contact surface is not real plane. The metal pressing ring or spacer surface is also not parallel to the lens surface. This kind of contact form will inevitably lead to point contact and line contact, which will cause a little bit high local pressure.

Why is athermalized design needed for the infrared optical system?

Temperature variation will result in changes in all parameters of the infrared system, which will influence its image plane position and image quality. Therefore, athermalized design is required. Generally, temperature affects the infrared system in the following three ways: 1.     The refractive indexes of the infrared optical components will change when the temperature changes. Under normal circumstances, the refractive indexes of the infrared optical components will change when temperature changes, which will change the focal length of the lens or the optical system.  The temperature coefficients of infrared optical materials are much larger than those of ordinary optical glass. For instance, the temperature coefficient value of K9 glass is only 2.8x10-6C-1, while that of the single crystal germanium dn/dt (a commonly used material for making infrared lenses) is 396x10-6C-1, about 141 times larger than the former. Therefore, the influence of temperature on the refractive index is quite apparent in the infrared system. 2.     The radius of curvature and the center thickness of the infrared optical components will change when the temperature changes. This change is caused by the fact that the material of the components expands on heating and contract on cooling, which is related to the optical material’s linear thermal expansion coefficient (a0). When the temperature changes, its radius of curvature and center thickness will turn into: D’=D+dD=D+D* a0*dT R’=R+dR=R+R* a0*dT Note: R and R’ are respectively its radius of curvature before and after temperature change; D and D’ are respectively its center thickness before and after the temperature change. dT refers to the temperature variation. 3.     The thermal effect of the lens tube material When the temperature changes, the dimensions of the assembly material will change, which will cause a change in the air gap between the optical components. Ultimately, it will influence the image quality. This change is associated with the assembly material’s linear expansion coefficient.   Among the above three main factors, the change of the refractive index of the optical material has the greatest influence on the image plane position and image quality; the influence of the radius of curvature is the second greatest, while changes in the thickness of optical components and the space between them have the least influence.    

How do the distance and angle affect the thermal imaging temperature measurement?

Without considering atmospheric transmittance and radiative transmission loss, A.    To the source point, the irradiance of the object at the source point is inversely proportional to the square of the distance. Although the radiation intensity of the source point does not change, the field angle between the source point and the thermal image becomes smaller as the distance between them increases. The figure below shows the relationship between the irradiance of the source point and the distance. Thus, when the distance increases, the measuring temperature will get obviously lower. A.    To the plane source object, if there is no angle between the target light source and the thermal imager at the same plane, and the instantaneous field of view in the measurement system is full of radiation energy, the distance change will make no difference in the result of thermal imaging temperature measurement. 

What are the main factors that can affect thermal imaging temperature measurement?

Many factors can affect thermal imaging temperature measurements, such as the emissivity of the target, the radiation temperature of the target, the atmospheric radiation temperature, the ambient reflection temperature, and other external factors; meanwhile, it is also affected by the lens temperature, the temperature of the detector array, the temperature of the inner thermal camera module, the temperature of the system circuit, and other internal factors. Moreover, in the actual temperature measurement process, the distance of the object and the angle also influence the measurement result.

What are the evaluation indices of Infrared Machine Core Focusing Functions?

1.Sensitivity. Near the peak of the focusing function, when the abscissa changes simultaneously, the y-coordinates of different focusing curves change to various degrees. The more significant is the y-coordinate variation near the peak value, the easier it is to find the real focal plane.2.Width of the Steep Region of the Curve. In the focusing process of the infrared lens, as it deviates further and further from the peak value, the image at first becomes increasingly blurred, and the function value decreases sharply until almost nothing can be seen distinctly; then, the curve becomes much flatter and the function value shows no significant change. We divide the focusing curve into steep and flat regions to represent this feature.In the steep region, the focusing function value changes sharply with the change of focusing distance indicated by the abscissa, while in the flat region, the function value virtually shows no change.3.Degree of Steepness. The first defocus stage and the second one of the infrared lens are different, because the front and the rear of the infrared detector have different depths of field and receive various amounts of radiation. Hence, the focusing curve does not show the same degree of steepness at the two sides of the peak value.4.Fluctuation Quantity of the Flat Region. The pattern of the focusing curve is influenced by the external radiated noise. Therefore, in a non-ideal state, the function value of the focusing curve will see some noticeable fluctuation in the flat region, and the quantity of such fluctuation is used to describe the degree of the fluctuation. This quantity can reflect the anti-noise ability of the focusing curve; the smaller the fluctuation volume (V) is, the more stable is the anti-noise ability of the function.5.Time. The computing time (T) represents the focusing speed of a function. The result of the calculation of each function is achieved by the test under specific conditions. Therefore, when the test conditions change, the result will change accordingly.

What are the current technical proposals for FOV stitching?

A. image space  stitching (internal  stitching) refers to the image  stitching using multiple detectors, which can be done directly, or by using optical elements. In both ways, inner stitching arranges the detectors in a certain order to form a whole receiving target plane. Some have proposed stitching by reflective prismatic decomposition, dividing the image plane into four parts which respectively belong to four detectors; it requires no moving components and thus maintains a compact structure. However, it necessitates a relatively long back focal length (BFL) to allow for the placement of the reflecting prism. Moreover, the energy efficiency would be low, and the lateral dimension of the system would be large. Within the infrared band, the focal planes of cooled detectors are enclosed in the Dewar flask, therefore, the direct stitching of the focal planes is inappropriate, and considering the lengths of the detectors, stitching by reflective prismatic decomposition or time-share pointing would require a larger BFL thus a longer overall structure.B. Object stitching (Outer stitching) is the stitching of the observation area in the object space. It involves the placement of multiple cameras in certain relative angles and positions to obtain an image of a large field of view. Each camera lens is responsive to a detector, for instance, “horizontal 1”, “vertical 1”, crisscross pattern, and “T” type. Some theses have put forward the crisscross pattern stitching of four surveying cameras to achieve the measurement of a large field of view. This is a simple arrangement, yet it requires cameras with the same optical parameters, and the optical parallax is inevitable, which brings about inaccuracy of FOV stitching. The cooled infrared detector is quite expensive, thus increasing the processing cost.

What are the current mid-wave and long-wave dual-band infrared imaging technologies?

1. Dual-detector and dual-band imaging technologyThe method uses two detectors with different wavelength bands and separate optical systems to construct dual-band imaging, and then obtains dual-band images through image registration and fusion technology.2. Dual-line and dual-band imaging technologyTwo-band detection line arrays are placed side by side on the same focal plane to obtain a line array detector that can detect dual-band radiation. At present, only the US Naval Research Laboratory has reported the research results of the dual-column dual-band imaging system in the open literature.3. Single-detector and dual-band imaging technologyThe development of dual-band detectors transferred from quantum wells to mercury cadmium telluride materials has accelerated and has begun to be commercialized.

How are infrared optical lenses designed and produced?

1. Determine the use band according to the usage scenario, system requirements, cost requirements, etc. Most of the occasions use a single band such as short wave, medium wave or long wave, but some special occasions need to use multiple bands. 2. After the band is determined, according to the overall performance requirements of the infrared system, the optical path layout is carried out, the technical parameters such as the focal length and the field of view of the infrared lens are determined, and the imaging quality requirements of the lens are determined at the same time.3. Select the initial structure form of the lens according to the performance index and optical path layout of the infrared optical lens. The initial structure is a typical structure form summed up in the case of a lot of design experience. The following is a brief list of a few: 4. Perform aberration correction and other optimizations on optical lenses through optical design software or other auxiliary tools. 5. Image quality evaluation of corrected and optimized optical solutions. 6. Calculate, assign and formulate processing tolerances and assembly tolerances of infrared optics components and assemblies.7. Draw infrared optical system diagrams, components and parts diagrams, etc. 8. All drawings are transferred to trial production drawings and start production trial production. 9. Test/debug the trial samples, issue test reports, optimize defects,10. Officially put into mass production and use.

How does the long EFL with large optics capabilities affect the DRI?

The focal length determines the field of view (FOV) of the thermal imaging camera. The longer the focal length, the smaller the FOV, which translates into more pixels across a target at a fixed range (meaning, the target angle divided by the IFOV angle).

What can Quanhom lens control board do for you?

A good assistant method for monitoring targets in thermal imaging by IR zooming lens with thermal imaging cores especially for long-distance surveillance and homeland security